Retrieves a list of custom user settings for a single user.
Custom settings provide a flexible way to store and retrieve custom user information that can be used in your own system.
###Getting Grouped Custom User Settings###
If the custom user settings you want to retrieve are grouped, you must include the following information in the header, after Content-Type, in the request:
group_name is your designated name for the group of customer user settings.
If the extra header information is not included, only the custom user settings that were added without a group are retrieved.
The external account number (int) or account ID GUID.
The ID of the user to access. Generally this is the ID of the current authenticated user, but if the authenticated user is an Administrator on the account,